Showerhead electrode assembly in a capacitively coupled plasma processing apparatus

ABSTRACT

A showerhead electrode assembly for use in a capacitively coupled plasma processing apparatus comprising a heat transfer plate. The heat transfer plate having independently controllable gas volumes which may be pressurized to locally control thermal conductance between a heater member and a cooling member such that uniform temperatures may be established on a plasma exposed surface of the showerhead electrode assembly.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/625,555, filed Sep. 24, 2012 for SHOWERHEAD ELECTRODE ASSEMBLY IN ACAPACITIVELY COUPLED PLASMA PROCESSING APPARATUS, the entire content ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to plasma processing apparatuses wherein a heattransfer plate is used to control temperature uniformity of a showerheadelectrode assembly supported in a capacitively coupled plasma processingapparatus.

BACKGROUND

Semiconductor substrate (“substrate”) fabrication often includesexposing a substrate to a plasma to allow the reactive constituents ofthe plasma to modify the surface of the substrate, e.g., remove materialfrom unprotected areas of the substrate surface. The substratecharacteristics resulting from the plasma fabrication process aredependent on the process conditions, including the plasmacharacteristics and substrate temperature. For example, in some plasmaprocesses a critical dimension, i.e., feature width, on the substratesurface can vary by about one nanometer per ° C. of substratetemperature. It should be appreciated that differences in substratetemperature between otherwise identical substrate fabrication processeswill result in different substrate surface characteristics. Thus, adrift in process results between different substrates can be caused byvariations in substrate temperature during plasma processing.Additionally, center-to-edge substrate temperature variations canadversely affect a die yield per substrate.

A general objective in substrate fabrication is to optimize a die yieldper substrate and fabricate each substrate of a common type in asidentical a manner as possible. To meet these objectives, it isnecessary to control fabrication parameters that influence the plasmaprocessing characteristics across an individual substrate and amongvarious substrates of a common type. Because plasma constituentreactivity is proportional to temperature, substrate temperature andplasma exposed surface temperatures can have a strong influence onplasma processing results across the substrate and among varioussubstrates. Therefore, a continuing need exists for improvements intemperature control during plasma fabrication processes.

SUMMARY

Disclosed herein is a showerhead electrode assembly of a plasmaprocessing chamber, comprising a showerhead electrode, a temperaturecontrolled top plate configured to support the showerhead electrode, aheater plate disposed between the temperature controlled top plate andthe showerhead electrode, and a heat transfer plate. The heat transferplate is disposed between the showerhead electrode and the temperaturecontrolled top plate, wherein the heat transfer plate comprises aplurality of independently controllable gas volumes defined to befluidly isolated from others of the plurality of independentlycontrollable gas volumes, such that a gas pressure within any given oneof the plurality of independently controllable gas volumes does notaffect another gas pressure within any other of the plurality ofindependently controllable gas volumes.

Additionally disclosed herein is a capacitively coupled plasmaprocessing apparatus comprising a vacuum chamber, a lower electrodeassembly adapted to receive a semiconductor substrate, and theshowerhead electrode assembly described above. At least one vacuum portis disposed in a bottom wall of the vacuum chamber and is connected toat least one vacuum pump operable to maintain the vacuum chamber at apredetermined vacuum pressure. A gas source supplies process gas throughthe showerhead electrode assembly to the vacuum chamber and an RF energysource is configured to energize the process gas into a plasma state.

Further disclosed herein is a method of processing a semiconductorsubstrate in a capacitively coupled plasma processing apparatus. Themethod comprises placing a semiconductor substrate on a top surface of alower electrode assembly inside the vacuum chamber. Each independentlycontrollable gas volume in the heat transfer plate is maintained at apredetermined pressure to effect a desired temperature distributionacross the plasma exposed surface of the showerhead electrode.Temperatures across the plasma exposed surface of the showerheadelectrode are determined and pressure in each independently controllablegas volume is adjusted to compensate for temperature gradients along theplasma exposed surface of the showerhead electrode. Process gas issupplied into the vacuum chamber from a gas supply, the gas is energizedinto a plasma state, and the semiconductor substrate is then etched withthe plasma.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 depicts an exemplary plasma processing apparatus that may be usedin accordance with preferred embodiments of the electrode assembliesdescribed herein.

FIG. 2A, B illustrate cross sections of preferred embodiments of ashowerhead electrode assembly.

FIG. 3A, B illustrate exemplary embodiments of a heat transfer plate.

DETAILED DESCRIPTION

Disclosed herein is a showerhead electrode assembly of a capacitivelycoupled plasma processing apparatus which will now be described indetail with reference to a few preferred embodiments thereof asillustrated in the accompanying drawings. In the following description,numerous specific details are set forth in order to provide a thoroughunderstanding of the present embodiments. It will be apparent, however,to one skilled in the art, that the present embodiments may be practicedwithout some or all of these specific details. In other instances, wellknown process steps and/or structures have not been described in detailin order to not unnecessarily obscure the present embodiments. As usedherein, the term “about” should be construed to include values up to 10%above or below the values recited.

FIG. 1 depicts an exemplary plasma processing apparatus 100 that can beused to practice preferred embodiments of the assemblies describedherein. The plasma processing apparatus is a capacitively coupled plasmaprocessing vacuum chamber, which can generate a plasma. The plasmaprocessing apparatus 100 comprises a vacuum chamber 102 which includes achamber wall 103. The inner surface of the chamber wall 103 ispreferably anodized aluminum and/or has a coating of plasma resistantmaterial such as a thermally sprayed yttria coating. The vacuum chamber102 includes a substrate transfer slot 118 provided in the chamber wall103 to transfer semiconductor substrates into and out of the vacuumchamber 102.

The vacuum chamber 102 can include a showerhead electrode assembly 104having a plasma exposed surface 108. The showerhead electrode assembly104 can have a single-piece electrode or a multi-piece electrode. Forexample, the showerhead electrode assembly 104 can have a single-piececonstruction including a showerhead electrode plate, or it can include ashowerhead electrode plate and an outer electrode ring. In such laterembodiments, both the showerhead electrode plate and the outer electrodering can be optionally backed by a plate of graphite or metal such asaluminum bonded thereto by a bonding material, such as an elastomermaterial, or fastened together with suitable fasteners. The showerheadelectrode assembly 104 can be sized to process 200 mm semiconductorsubstrates, 300 mm substrates, or even larger substrates for example.The showerhead electrode plate of the showerhead electrode assembly 104(including the outer electrode ring in multi-piece constructions) can beof silicon (e.g., single crystalline silicon, polycrystalline silicon oramorphous silicon) or silicon carbide. The apparatus 100 includes a gassource (not shown) for supplying process gas to the showerhead electrodeassembly 104. The showerhead electrode assembly 104 is preferablypowered by an RF supply 106 via a matching network. In anotherembodiment, the showerhead electrode plate of the showerhead electrodeassembly 104 can be grounded to provide a return path for power suppliedby a bottom electrode comprised in a substrate support 111 of the vacuumchamber 102, as described below.

In the embodiment of the apparatus 100 shown in FIG. 1, process gas issupplied into the vacuum chamber 102 at the plasma region developedbetween the showerhead electrode assembly 104 and a semiconductorsubstrate 10 supported on the substrate support 111. The substratesupport 111 preferably includes an electrostatic chuck 114 (“ESC”) thatsecures the semiconductor substrate 10 on the substrate support 111 byan electrostatic clamping force. In an embodiment, the ESC 114 may actas a bottom electrode and is preferably biased by an RF power source 116(typically via a matching network). The upper surface 115 of the ESC 114preferably has approximately the same diameter as the semiconductorsubstrate 10.

In an embodiment the ESC 114 may further include an embedded temperaturecontrol module comprising a plurality of channels (not shown) to provideheating/cooling zones. An exemplary temperature control module that canbe used may be found in commonly owned U.S. Pat. No. 8,083,855, which ishereby incorporated by reference in its entirety.

The substrate support 111 may further include at least one temperaturesensor 150 for measuring temperatures across a plasma exposed surface108 of the showerhead electrode assembly 104. The temperature sensor 150may be a laser interferometer or other suitable sensor, and ispreferably connected to a controller for processing temperaturemeasurements taken by said sensor. In alternate embodiments thetemperature sensor 150 may be incorporated in the showerhead electrodeassembly 104.

The vacuum chamber 102 may comprise at least one vacuum port (not shown)connected to at least one vacuum pump (not shown). The vacuum pump isadapted to maintain a predetermined vacuum pressure inside the vacuumchamber 102. Process gas and reaction by-products are drawn by the pumpgenerally in the direction represented by arrows 110.

An exemplary capacitively coupled plasma reactor that can be used is adual-frequency plasma etch reactor (see, e.g., commonly-assigned U.S.Pat. No. 6,090,304, which is hereby incorporated by reference in itsentirety). In such reactors, etching gas can be supplied to theshowerhead electrode from a gas supply and a plasma can be generated inthe reactor by supplying RF energy from two RF sources to the showerheadelectrode and/or a bottom electrode, or the showerhead electrode can beelectrically grounded and RF energy at two different frequencies can besupplied to the bottom electrode.

FIG. 2A illustrates a cross section of an embodiment of the showerheadelectrode assembly 104 to be used in a capacitively coupled plasmachamber comprising a showerhead electrode 303 and an optional backingmember 302 secured to the showerhead electrode 303, a heater plate 304,and a temperature controlled top plate 301. The heater plate 304 canhave an optional outer heater member 304 a. The showerhead electrode 303is positioned above a substrate support 111 (see FIG. 1) supporting asemiconductor substrate 10.

The temperature controlled top plate 301 can form a removable top wallof the plasma processing apparatus. The showerhead electrode 303 caninclude an inner electrode member, and an optional outer electrodemember (not shown). The inner electrode member is typically made ofsingle crystal silicon. If desired, the inner and outer electrodes canbe made of a single piece of material such as CVD silicon carbide,single crystal silicon or other suitable material.

The inner electrode member can have a diameter smaller than, equal to,or larger than a semiconductor substrate to be processed, e.g., up to200 mm. For processing larger semiconductor substrates such as 300 mmsubstrates or larger, the outer electrode member is adapted to expandthe diameter of the showerhead electrode 303. The outer electrode membercan be a continuous member (e.g., a poly-silicon or silicon carbidemember, such as a ring), or a segmented member (e.g., 2-6 separatesegments arranged in a ring configuration, such as segments of singlecrystal silicon). Alternatively, the showerhead can be a monolithicpart.

The showerhead electrode 303 preferably includes multiple gas passagesfor injecting a process gas into a space in the vacuum chamber 102 belowthe showerhead electrode 303. The outer electrode preferably may form araised step at the periphery of the showerhead electrode 303. Furtherdetails of a stepped electrode can be found in commonly-owned U.S. Pat.No. 6,824,627, the disclosure of which is hereby incorporated byreference.

In an embodiment the showerhead electrode assembly 104 includes a heattransfer plate 220 for controlling heat transfer in the showerheadelectrode assembly 104. The heat transfer plate 220 is disposed betweenthe heater plate 304 and the temperature controlled top plate 301 and isadapted to contain a heat transfer gas which can be pressurized toincrease thermal conductance between the heater plate 304 and thetemperature controlled top plate 301. In an alternate embodiment, asillustrated in FIG. 2B, the heat transfer plate 220 may be disposedbetween the heater plate 304 and the showerhead electrode 303. The heattransfer plate 220 comprises a plurality of gas volumes wherein each gasvolume is independently controllable such that a gas pressure within anygiven gas volume does not affect another gas pressure within any otherof the plurality of independently controlled gas volumes.

When the independently controllable gas volumes in the heat transferplate 220 undergo an increase in gas pressure, thermal coupling betweenelements adjacent to the heat transfer plate 220, such as for example,the temperature controlled top plate and the heater plate, increases aswell. The increase in thermal coupling may be utilized to quickly heatthe showerhead electrode assembly 104 to prepare for semiconductorsubstrate processing, or may be used to compensate for thermal gradientsacross the plasma exposed surface of the showerhead electrode assembly104 and provide more uniform etch results. Additionally, gas may beevacuated from the independently controllable gas volumes of the heattransfer plate 220, wherein the heat transfer plate 220 will act as aninsulator, and temperatures in the showerhead electrode assembly 104 maybe maintained.

The plurality of independently controllable gas volumes can hold apressurized heat transfer gas, for example, helium, neon, argon,nitrogen, or a mixture thereof. Preferably, the heat transfer gas usedis helium. Gas conduits (not shown) are provided within the temperaturecontrolled top plate 301 to be in fluid communication with each of theindependently controllable gas volumes. During the plasma process, theheat transfer gas can be supplied or exhausted via the gas conduits, toachieve a specified gas pressure within the plurality of independentlycontrollable gas volumes.

The gas volumes are preferably arranged to extend radially and/orcircumferentially across at least part of the heat transfer plate 220.By controlling the gas pressure within each of the plurality ofindependently controllable gas volumes, and hence thermal conductivity,between the temperature controlled top plate 301 and the heater plate304, or alternatively the heater plate 304 and the showerhead electrode303, a prescribed radial temperature gradient can be established on theplasma exposed surface of the showerhead electrode 303. In oneembodiment, the gas pressure within a particular independentlycontrollable gas volume can be controlled within a range extending fromabout 0 torr to about 1 atm. Preferably, the gas pressure within aparticular independently controllable gas volume is within a rangeextending from about 0 torr to 10 torr. In one embodiment, helium gas issupplied to the various gas volumes. However, in other embodiments,other types of gas or gas mixtures, e.g., nitrogen, can be supplied thevarious gas volumes.

FIG. 3A, B illustrate top views of embodiments of the heat transferplate 220. The heat transfer plate comprises a plurality ofindependently controllable gas volumes defined to be fluidly isolatedfrom others of the plurality of independently controllable gas volumes.The gas pressure within any given one of the plurality of independentlycontrollable gas volumes does not affect another gas pressure within anyother of the plurality of independently controllable gas volumes.

As shown in FIG. 3A, the heat transfer plate 220 can comprise sixteenradially extending independently controllable gas volumes. Eight of thegas volumes are located in an inner region 401 of the heat transferplate 220 and the remaining eight gas volumes are located in an outerregion 402 of the heat transfer plate. Each independently controllablegas volume extends about 38 to 45° around the circumference of the heattransfer plate 220.

FIG. 3B illustrates the heat transfer plate 220 wherein the heattransfer plate 220 comprises a first cylindrical independentlycontrollable gas volume 420 located at the center of the heat transferplate 220 and three concentric annular independently controllable gasvolumes 421 a,b,c radially outward of the first cylindricalindependently controllable gas volume. It will be apparent, however, toone skilled in the art that the heater transfer plate 220 may have moreor less than three concentric annular independently controllable gasvolumes.

Additionally, although the heat transfer plate 220 is described ashaving radially extending temperature control volumes (see FIG. 3A), itshould be appreciated that in other embodiments the variousindependently controllable gas volumes within the heat transfer plate220 can be defined to correspond to non-radial geometric configurations.For example, in other embodiments, the various gas volumes within theheat transfer plate 220 can be defined in a hexagonally dividedconfiguration or in a quadrant divided configuration.

The heat transfer plate 220 can locally increase or decrease thermalconductance between the heater plate 304 and the temperature controlledtop plate 301, or alternatively, the heater plate 304 and the showerheadelectrode 303 in the showerhead electrode assembly. Greater control overthermal conductance in the showerhead electrode assembly allows moreuniform temperatures to be attained across the plasma exposed surface ofthe showerhead electrode assembly in the plasma processing apparatus.

Referring back to FIG. 1, the semiconductor substrate 10 is processed inthe capacitively coupled plasma processing apparatus 100. The method ofprocessing comprises placing the semiconductor substrate 10 on a topsurface 113 of the substrate support 11 inside the vacuum chamber 102.Next each independently controllable gas volume in the heat transferplate 202 is pressurized to a predetermined pressure to attain a desiredtemperature profile across the plasma exposed surface 108 of theshowerhead electrode assembly 104. Then measurements of the temperatureacross the plasma exposed surface 108 of the showerhead electrodeassembly 104 are determined and the pressure in each independentlycontrollable gas volume is adjusted in-situ to compensate fortemperature gradients across the plasma exposed surface of theshowerhead electrode. A process gas is then supplied into the vacuumchamber 102 from a gas supply, the process gas is energized into aplasma state, and the semiconductor substrate is etched with the plasma.

In alternate embodiments, the temperature gradient across the plasmaexposed surface 108 is measured while etching, and in-situ adjustmentsof the pressure in each independently controllable gas volume iseffectuated to increase uniformity of the etching by reducingtemperature gradients along the plasma exposed surface 108 of theshowerhead electrode assembly 104.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A showerhead electrode assembly of a plasmaprocessing chamber, comprising: a showerhead electrode; a top plateconfigured to support the showerhead electrode; a heater plate disposedbetween the top plate and the showerhead electrode; and a heat transferplate disposed between the showerhead electrode and the top plate,wherein the heat transfer plate comprises a plurality of independentlycontrollable gas volumes such that a gas pressure within any given oneof the plurality of independently controllable gas volumes does notaffect another gas pressure within any other of the plurality ofindependently controllable gas volumes.
 2. The showerhead electrodeassembly of claim 1, wherein the heat transfer plate is disposed betweenthe top plate and the heater plate.
 3. The showerhead electrode assemblyof claim 1, wherein the heat transfer plate is disposed between theheater plate and the showerhead electrode.
 4. The showerhead electrodeassembly of claim 1, wherein the independently controllable gas volumeshave a radial configuration, a non-radial configuration, a hexagonallydivided configuration, an octagonally divided configuration, or aquadrant divided configuration.
 5. The showerhead electrode assembly ofclaim 1, wherein the heat transfer plate comprises sixteen radiallyextending independently controllable gas volumes wherein eight gasvolumes are located in an inner region of the heat transfer plate andeight gas volumes are located in an outer region of the heat transferplate, each independently controllable gas volume extending about 38 to45° around the circumference of the heat transfer plate.
 6. Theshowerhead electrode assembly of claim 1, wherein the heat transferplate comprises a first cylindrical independently controllable gasvolume and three concentric annular independently controllable gasvolumes radially outward of the first cylindrical independentlycontrollable gas volume.
 7. The showerhead electrode assembly of claim1, wherein a gas can be supplied to the independently controllable gasvolumes of the heat transfer plate selected from helium, neon, argon,nitrogen, or a mixture thereof.
 8. The showerhead electrode assembly ofclaim 1, further comprising at least one sensor, the at least one sensorconfigured to determine a temperature gradient across a plasma exposedsurface of the showerhead electrode during use thereof.
 9. Theshowerhead electrode assembly of claim 1, wherein each of theindependently controllable gas volumes may be pressurized in a range ofabout 0 torr to about 1 atm.
 10. The showerhead electrode assembly ofclaim 1, wherein each of the independently controllable gas volumes maybe pressurized in a range of about 0 torr to about 10 torr.
 11. Acapacitively coupled plasma processing apparatus comprising: a vacuumchamber; a lower electrode assembly adapted to receive a semiconductorsubstrate; the showerhead electrode assembly of claim 1; at least onevacuum port in a bottom wall connected to at least one vacuum pumpoperable to maintain the vacuum chamber at a predetermined vacuumpressure; a gas source operable to supply process gas through theshowerhead electrode assembly to the vacuum chamber; and an RF energysupply configured to energize the process gas into a plasma state. 12.The capacitively coupled plasma processing apparatus of claim 11,wherein the heat transfer plate is disposed between the top plate andthe heater plate or the heat transfer plate is disposed between theheater plate and the showerhead electrode.
 13. The capacitively coupledplasma processing apparatus of claim 11, wherein the independentlycontrollable gas volumes of the heat transfer plate have a radialconfiguration, a non-radial configuration, a hexagonally dividedconfiguration, an octagonally divided configuration, or a quadrantdivided configuration.
 14. The capacitively coupled plasma processingapparatus of claim 11, wherein the heat transfer plate comprises sixteenradially extending independently controllable gas volumes wherein eightgas volumes are located in an inner region of the heat transfer plateand eight gas volumes are located in an outer region of the heattransfer plate, each independently controllable gas volume extendingabout 38 to 45° around the circumference of the heat transfer plate. 15.The capacitively coupled plasma processing apparatus of claim 11,wherein the heat transfer plate comprises a first cylindricalindependently controllable gas volume and three concentric annularindependently controllable gas volumes radially outward of the firstcylindrical independently controllable gas volume.
 16. The capacitivelycoupled plasma processing apparatus of claim 11, wherein each of theindependently controllable gas volumes may be pressurized in a range ofabout 0 torr to about 1 atm.
 17. The capacitively coupled plasmaprocessing apparatus of claim 11, wherein each of the independentlycontrollable gas volumes may be pressurized in a range of about 0 torrto about 10 torr.
 18. The capacitively coupled plasma processingapparatus of claim 11, further comprising at least one sensor, the atleast one sensor configured to determine the temperature gradient acrossa plasma exposed surface of the showerhead electrode during use thereof.19. A method of etching a semiconductor substrate in a capacitivelycoupled plasma processing apparatus using the capacitively coupledplasma processing apparatus of claim 11, comprising: placing asemiconductor substrate on a top surface of the lower electrode assemblyinside the vacuum chamber; pressurizing each independently controllablegas volume in the heat transfer plate comprised in the showerheadelectrode assembly to a predetermined pressure to effect a desiredtemperature profile across the plasma exposed surface of the showerheadelectrode; measuring at least one temperature across the plasma exposedsurface of the showerhead electrode; adjusting in-situ the pressure ineach independently controllable gas volume to compensate for temperaturegradients across the plasma exposed surface of the showerhead electrode;supplying a gas into the vacuum chamber from a gas supply; andenergizing the gas into a plasma state and etching the semiconductorsubstrate with the plasma.
 20. The method of claim 19, furthercomprising measuring the temperature gradient across the plasma exposedsurface while etching, and adjusting in-situ the pressure in eachindependently controllable gas volume to effectuate more uniform etchingby reducing temperature gradients along the plasma exposed surface ofthe showerhead electrode.